Wide-angle zoom lens system

ABSTRACT

A wide-angle zoom lens system includes a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in this order from the object. Upon zooming from the short focal length extremity to the long focal length extremity, a distance between the negative first lens group and the positive second lens group decreases, a distance between the positive second lens group and the negative third lens group increases, and a distance between the negative third lens group and the positive fourth lens group decreases. The wide-angle zoom lens system satisfies the following conditions: 
 
1.6&lt; X 2/ fw &lt;3.5  (1) 
 
1.2&lt;| f 1|/ fw &lt;2.0 (f1&lt;0)  (2) 
 
1.6&lt; f 2/ fw &lt;2.7  (3) 
wherein X2: the traveling distance of the positive second lens group upon zooming from the short focal length extremity to the long focal length extremity; f1: the focal length of the negative first lens group; f2: the focal length of the positive second lens group; and fw: the focal length of the entire wide-angle zoom lens system at the short focal length extremity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wide-angle zoom lens system which issuitable for a single-lens reflex (SLR) camera, and especially suitablefor a digital single-lens reflex camera.

2. Description of the Prior Art

In a digital SLR camera, the size of the imaging device is smaller thana frame size of the film for a silver-halide SLR camera. Therefore anoptical system having a wider angle-of-view (shorter focal length) isnecessary.

For example, a zoom lens system of a two-lens-group arrangement (e.g.,negative and positive lens groups) has been commonly used; or a zoomlens system of a four-lens-group arrangement (e.g., negative, positive,negative and positive lens groups) has also been commonly used. Zoomlens systems of these types have been disclosed in Japanese UnexaminedPatent Publication (hereinafter, JUPP) No. H10-325923, JUPP No.H11-174328, JUPP No. 2004-240038, and JUPP No. 2002-287031,

The majority of conventional wide-angle zoom lens systems have a zoomratio of approximately 2. Even in the case where a zoom lens system hasa zoom ratio of more than 2, a wide-angle zoom lens system, used with animaging device having a smaller image plane like that of APSC size imagesensors, has not been known to have an angle-of-view of more than 100degrees.

In JUPP No. H10-325923, the wide-angle zoom lens system has a sufficientangle-of-view of closer to 100 degrees; however, the zoom ratio is lessthan 2.

In JUPP No. 11-174328, the wide-angle zoom lens system has a zoom ratioof approximately 2.8; however, a sufficient angle-of-view cannot beachieved.

In JUPP No. 2004-240038 and JUPP No. 2002-287031, the wide-angle zoomlens systems have the zoom ratio is approximately 2.2, i.e.,substantially equal to 2, and the angle-of-view is insufficient.

SUMMARY OF THE INVENTION

The present invention achieves a wide-angle zoom lens system which issuitable for a digital SLR camera having a smaller imaging device, has awide angle-of-view of approximately 100 degrees at the short focallength extremity, and has a zoom ratio of approximately 2.5 to 3.0.

According to an aspect of the present invention, there is provided awide-angle zoom lens system including a first lens group having anegative refractive power (hereinafter, a negative first lens group), asecond lens group having a positive refractive power (hereinafter, apositive second lens group), a third lens group having a negativerefractive power (hereinafter, a negative third lens group) and a fourthlens group having a positive refractive power (hereinafter, a positivefourth lens group), in this order from the object.

Upon zooming from the short focal length extremity to the long focallength extremity, a distance between the negative first lens group andthe positive second lens group decreases, a distance between thepositive second lens group and the negative third lens group increases,and a distance between the negative third lens group and the positivefourth lens group decreases.

The wide-angle zoom lens system satisfies the following conditions:1.6<X2/fw<3.5  (1)1.2<|f1|/fw<2.0 (f1<0)  (2)1.6<f2/fw<2.7  (3)

wherein

X2 designates the traveling distance of the positive second lens groupupon zooming from the short focal length extremity to the long focallength extremity;

f1 designates the focal length of the negative first lens group;

f2 designates the focal length of the positive second lens group; and

fw designates the focal length of the entire wide-angle zoom lens systemat the short focal length extremity.

The wide-angle zoom lens system preferably satisfies the followingcondition:0.9<X2/f2<1.6  (4)

wherein

X2 designates the traveling distance of the positive second lens groupupon zooming from the short focal length extremity to the long focallength extremity; and

f2 designates the focal length of the positive second lens group.

The wide-angle zoom lens system preferably satisfies the followingconditions:2.0<fBw×fBw/(f1×f3)<6.0  (5)1.2<f2/|f1|<1.8  (6)1.0<f4/|f3|<1.8  (7)

wherein

fBw designates the equivalent air thickness from the most image-sidelens surface to the image plane at the short focal length extremity;

f1 designates the focal length of the negative first lens group;

f2 designates the focal length of the positive second lens group;

f3 designates the focal length of the negative third lens group; and

f4 designates the focal length of the positive fourth lens group.

Furthermore, the wide-angle zoom lens system preferably satisfies thefollowing conditions:0.5<f1/f3<0.9  (8)0.6<f2/f4<0.9  (9)

According to another aspect of the present invention, there is provideda wide-angle zoom lens system including a negative first lens group, apositive second lens group, a negative third lens group and a positivefourth lens group, in this order from the object.

Upon zooming from the short focal length extremity to the long focallength extremity, a distance between the negative first lens group andthe positive second lens group decreases, a distance between thepositive second lens group and the negative third lens group increases,and a distance between the negative third lens group and the positivefourth lens group decreases.

The wide-angle zoom lens system satisfies the following conditions:2.0<fBw×fBw/(f1×f3)<6.0  (5)1.2<f2/|f1|<1.8  (6)1.0<f4/|f3|<1.8  (7)

wherein

fBw designates the equivalent air thickness from the most image-sidelens surface to the image plane at the short focal length extremity;

f1 designates the focal length of the negative first lens group;

f2 designates the focal length of the positive second lens group;

f3 designates the focal length of the negative third lens group; and

f4 designates the focal length of the positive fourth lens group.

The negative first lens group preferably includes a negative meniscuslens element having the convex surface facing toward the object, anothernegative meniscus lens element having the convex surface facing towardthe object, a negative lens element having a concave surface facingtoward the image, and a positive lens element, in this order from theobject.

The negative first lens group preferably includes a positive lenselement, a negative meniscus lens element having the convex surfacefacing toward the object, another negative meniscus lens element havinga convex surface facing toward the object, a negative lens elementhaving the concave surface facing toward the image and a positive lenselement, in this order from the object.

The positive second lens group preferably includes positive cementedlens elements and a positive lens element.

The negative third lens group preferably includes negative cemented lenselements and a positive lens element, or, two sets of negative cementedlens elements.

The positive fourth lens group preferably includes cemented lenselements and two positive lens elements.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2005-190539 (filed on Jun. 29, 2006) which isexpressly incorporated herein in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed below in detail with referenceto the accompanying drawings, in which:

FIG. 1 is a lens arrangement of the wide-angle zoom lens system, at theshort focal length extremity, according to a first embodiment of thepresent invention;

FIGS. 2A, 2B, 2C, 2D and 2E show aberrations occurred in the lensarrangement shown in FIG. 1;

FIG. 3 is a lens arrangement of the wide-angle zoom lens system, at thelong focal length extremity, according to the first embodiment of thepresent invention;

FIGS. 4A, 4B, 4C, 4D and 4E show aberrations occurred in the lensarrangement shown in FIG. 3;

FIG. 5 is a lens arrangement of the wide-angle zoom lens system, at theshort focal length extremity, according to a second embodiment of thepresent invention;

FIGS. 6A, 6B, 6C, 6D and 6E show aberrations occurred in the lensarrangement shown in FIG. 5;

FIG. 7 is a lens arrangement of the wide-angle zoom lens system, at thelong focal length extremity, according to the second embodiment of thepresent invention;

FIGS. 8A, 8B, 8C, 8D and 8E show aberrations occurred in the lensarrangement shown in FIG. 7;

FIG. 9 is a lens arrangement of the wide-angle zoom lens system, at theshort focal length extremity, according to a third embodiment of thepresent invention;

FIGS. 10A, 10B, 10C, 10D and 10E show aberrations occurred in the lensarrangement shown in FIG. 9;

FIG. 11 is a lens arrangement of the wide-angle zoom lens system, at thelong focal length extremity, according to the third embodiment of thepresent invention;

FIGS. 12A, 12B, 12C, 12D and 12E show aberrations occurred in the lensarrangement shown in FIG. 11;

FIG. 13 is a lens arrangement of the wide-angle zoom lens system, at theshort focal length extremity, according to a fourth embodiment of thepresent invention;

FIGS. 14A, 14B, 14C, 14D and 14E show aberrations occurred in the lensarrangement shown in FIG. 13;

FIG. 15 is a lens arrangement of the wide-angle zoom lens system, at thelong focal length extremity, according to the fourth embodiment of thepresent invention;

FIGS. 16A, 16B, 16C, 16D and 16E show aberrations occurred in the lensarrangement shown in FIG. 15;

FIG. 17 is a lens arrangement of the wide-angle zoom lens system, at theshort focal length extremity, according to a fifth embodiment of thepresent invention;

FIGS. 18A, 18B, 18C, 18D and 18E show aberrations occurred in the lensarrangement shown in FIG. 17;

FIG. 19 is a lens arrangement of the wide-angle zoom lens system, at thelong focal length extremity, according to the fifth embodiment of thepresent invention;

FIGS. 20A, 20B, 20C, 20D and 20E show aberrations occurred in the lensarrangement shown in FIG. 19; and

FIG. 21 is the schematic view of the lens-group moving paths for thewide-angle zoom lens system according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The wide-angle zoom lens system of the present invention, as shown inthe zoom path of FIG. 21, includes a negative first lens group 10, apositive second lens group 20, a negative third lens group 30, and apositive fourth lens group 40, in this order from the object.

Upon zooming from the short focal length extremity (W) to the long focallength extremity (T), the negative first lens group 10 first movestoward the image and thereafter and moves toward the object; thepositive second lens group 20, the negative third lens group 30 and thepositive fourth lens group 40 move monotonically toward the object.

While the zooming is being performed, the distance between the negativefirst lens group 10 and the positive second lens group 20 firstdecreases largely, and thereafter gradually decreases; the distancebetween the positive second lens group 20 and the negative third lensgroup 30 monotonically increases; the distance between the negativethird lens group 30 and the positive fourth lens group 40 monotonicallydecreases; and the distance between the positive fourth lens group 40and the image plane monotonically increases.

A diaphragm S is arranged to move together with the positive second lensgroup 20 or the third lens group 30.

Condition (1) specifies the ratio of the traveling distance of thepositive second lens group 20 upon zooming from the short focal lengthextremity to the long focal length extremity to the focal length of theentire wide-angle zoom lens system at the short focal length extremity.

If the traveling distance of the positive second lens group 20 becomeslonger to the extent that X2/fw exceeds the upper limit of condition(1), the distance between the negative third lens group 30 and thepositive fourth lens group 40 at the short focal length extremity has tobe made shorter in order to prevent an increase in the overall length ofthe wide-angle zoom lens system.

The negative third lens group 30 is arranged to function to effectivelycorrect aberrations with respect to each focal length by relativelyvarying the distance between the negative third lens group 30 and thepositive fourth lens group 40 upon zooming. Therefore if the amount ofchange in the relatively-varying distance therebetween becomesinsufficient, the effect of the correcting of aberrations cannot beadequately obtained.

On the other hand, if an attempt is made to obtain a sufficient zoomratio while the traveling distance of the positive second lens group 20maintains shorter to the extent that X2/fw exceeds the lower limit ofcondition (1), the refractive power (hereinafter, power) of the positivesecond lens group 20 has to be made stronger. Consequently, aberrations,such as spherical aberration, become larger. In such a case, thewide-angle zoom lens system preferably satisfies the followingcondition:1.7<X2/fw<3.5  (1′)

Condition (2) specifies the ratio of the focal length of the negativefirst lens group 10 to the focal length of the entire wide-angle zoomlens system at the short focal length extremity.

If the negative power of the negative first lens group 10 becomes weakerto the extent that |f1|/fw exceeds the upper limit of condition (2), thenegative power of the negative third lens group 30 has to be madestronger to attain a predetermined back focal distance. Consequently,spherical aberration and coma are overcorrected.

If the negative power of the negative first lens group 10 becomestronger to the extent that |f1|/fw exceeds the lower limit of condition(2), distortion and astigmatism become larger at the short focal lengthextremity. Moreover, a suitable telephoto state cannot be attained atthe long focal length extremity. Accordingly, the positive second lensgroup 20 is required to have a stronger positive power in order to makethe overall length of the wide-angle zoom lens system shorter at thelong focal length extremity; and spherical aberration occurs largely atthe long focal length extremity.

Condition (3) specifies the ratio of the focal length of the positivesecond lens group 20 to the focal length of the entire wide-angle zoomlens system at the short focal length extremity.

If the positive power of the positive second lens group 20 becomesweaker to the extent that f2/fw exceeds the upper limit of condition(3), the correcting of distortion and astigmatism occurred in thenegative first lens group 10 cannot be sufficiently made at the shortfocal length extremity in particular.

If the positive power of the positive second lens group 20 becomesstronger to the extent that f2/fw exceeds the lower limit of condition(3), spherical aberration and coma largely occur at the long focallength extremity. In such a case, the wide-angle zoom lens systempreferably satisfies the following condition:1.8<f2/fw<2.5  (3′)

Condition (4) specifies the ratio of the traveling distance of thepositive second lens group 20 upon zooming from the short focal lengthextremity to the long focal length extremity to the focal length of thepositive second lens group 20.

If the traveling distance of the positive second lens group 20 becomeslonger, or, if the positive power of the positive second lens group 20becomes stronger, to the extent that X2/f2 exceeds the upper limit ofcondition (4), fluctuation of aberrations due to zooming becomes larger.Consequently, adequate optical performance of the wide-angle zoom lenssystem cannot be maintained over the entire zooming range.

If the traveling distance of the positive second lens group 20 becomesshorter, or, if the positive power of the positive second lens group 20becomes weaker, to the extent that X2/f2 exceeds the lower limit ofcondition (4), a sufficient zoom ratio cannot be attained.

Condition (5) concerns the balance among the focal length of thenegative first lens group 10, that of the negative third lens group 30,and the back focal distance at the short focal length extremity.

If fBw×fBw/(f1×f3) exceeds the upper limit of condition (5), thenegative refractive power in the wide-angle zoom lens system becomesstronger, so that it is advantageous to secure the back focal distance.However, the correcting of distortion and astigmatism at the short focallength extremity becomes difficult. Furthermore, spherical aberration atthe long focal length extremity is overcorrected.

If fBw×fBw/(f1×f3) exceeds the lower limit of condition (5), thenegative power in the wide-angle zoom lens system becomes insufficient,so that it is difficult to secure a predetermined back focal distance.Moreover, it is necessary to make the traveling distance of each lensgroup longer for the purpose of securing the back focal distance.Consequently, the change in spherical aberration and coma upon zoomingbecomes larger. In such a case, the wide-angle zoom lens systempreferably satisfies the following condition:2.8<fBw×fBw/(f1×f3)<4.5  (5′)

Condition (6) specifies the ratio of the focal length of the positivesecond lens group 20 to that of the negative first lens group 10.

If f2/|f1| exceeds the upper limit of condition (6), the power of thenegative first lens group 10 becomes too strong. Consequently, thecorrecting of distortion and astigmatism at the short focal lengthextremity cannot be adequately made.

If f2/|f1| exceeds the lower limit of condition (6), the power of thepositive second lens group 20 becomes too strong. Consequently, thecorrecting of spherical aberration and coma becomes difficult at thelong focal length extremity in particular. In such a case, thewide-angle zoom lens system preferably satisfies the followingcondition:1.2<f2|f1|<1.6  (6′)

Condition (7) specifies the ratio of the focal length of the positivefourth lens group 40 to that of the negative third lens group 30.

If f4/|f3| exceeds the upper limit of condition (7), the power of thenegative third lens group 30 becomes too strong. Consequently, sphericalaberration and coma are overcorrected at the long focal length extremityin particular.

If f4/|f3| exceeds the lower limit of condition (7), the power of thepositive fourth lens group 40 becomes too strong. Consequently, thecorrecting of coma at the long focal length extremity and the correctingof distortion at the short focal length extremity cannot be madesuitably. In such a case, the wide-angle zoom lens system preferablysatisfies the following condition:1.2<f4/|f3|<1.6  (7′)

Condition (8) specifies the ratio of the focal length of the negativefirst lens group 10 to that of the negative third lens group 30.

If f1/f3 exceeds the upper limit of condition (8), the power of thenegative third lens group 30 becomes too strong. Consequently, sphericalaberration becomes overcorrected at the long focal length extremity inparticular.

If f1/f3 exceeds the lower limit of condition (8), the power of thenegative first lens group 10 becomes too strong. Consequently, thecorrecting of distortion and astigmatism at the short focal lengthextremity cannot be adequately made.

Condition (9) specifies the ratio of the focal length of the positivesecond lens group 20 to that of the positive fourth lens group 40.

If f2/f4 exceeds the upper limit of condition (9), the power of thepositive fourth lens group 40 becomes too strong. Consequently, thecorrecting of coma at the long focal length extremity and the correctingof distortion at the short focal length extremity cannot be adequatelymade.

If f2/f4 exceeds the lower limit of condition (9), the power of thepositive second lens group 20 becomes too strong. Consequently, thecorrecting of spherical aberration and coma at the long focal lengthextremity in particular cannot be made adequately.

The negative first lens group 10 can include a (first) negative meniscuslens element having the convex surface facing toward the object, another(second) negative meniscus lens element having the convex surface facingtoward the object, a negative lens element having a concave surfacefacing toward the image, and a positive lens element, in this order fromthe object.

Furthermore, the negative first lens group 10 can include a (first)negative meniscus lens element having the convex surface facing towardthe object, another (second) negative meniscus lens element having theconvex surface facing toward the object, a positive lens element, anegative lens element having a concave surface facing toward the image,and another positive lens element, in this order from the object.

In the negative first lens group 10, an aspherical surface is formed onthe most object-side lens element (i.e., the negative meniscus lenselement having the convex surface facing toward the object). Due to thisarrangement, the correcting of distortion and astigmatism occurred inthe wide-angle zoom lens system can be made suitably. The asphericalsurface is formed so that the negative power becomes weaker toward theperiphery of the lens element. In the case where the aspherical surfaceis formed on the object-side surface of the most object-side lenselement in the negative first lens group 10, the correcting ofdistortion in particular can be made suitably. On the other hand, in thecase where the aspherical surface is formed on the image-side surface ofthe most object-side lens element in the negative first lens group 10,the thickness (the distance from the center on the object-side surfaceto the peripheral edge of the image-side thereof) of the mostobject-side lens element can be made thinner.

In the negative first lens group 10, a positive lens element can beprovided on the object side of the (first) meniscus lens element. Thepositive lens element is preferably a biconvex positive lens element.

In other words, the negative first lens group 10 can include a biconvexpositive lens element, a (first) negative meniscus lens element havingthe convex surface facing toward the object, another (second) negativemeniscus lens element having the convex surface facing toward theobject, a negative lens element having a concave surface facing towardthe image, and a positive lens element, in this order from the object.

If the second negative meniscus lens element is formed as a syntheticresin aspherical lens element, the correcting of distortion andastigmatism becomes possible.

Furthermore, by positioning the biconvex positive lens element at themost object-side of the wide-angle zoom lens system, distortion occurredin the second negative meniscus lens element which is made of syntheticresin can be corrected.

Since a lens element made of synthetic resin has poor durability, it isnot preferable to provide such a lens element at the most object-side ofthe zoom lens system. Moreover, if the diameter of such a lens elementbecomes too large, the peripheral-edge thickness thereof becomesthicker. Consequently, fluctuations in aberration due to temperaturechanges become undesirably noticeable.

Therefore it is appropriate to form a relatively smaller diameter lenselement as a synthetic resin lens element. If this is applied to thenegative first lens group 10, the second negative meniscus lens elementis suitable to be formed as a synthetic resign lens element. If thesurface having a smaller curvature is made aspherical, the curvature atthe periphery can be made larger. Consequently, the change inaberrations due to the temperature change can be made smaller.

The positive second lens group 20 can include positive cemented lenselements and a positive lens element. More specifically, the positivesecond lens group 20 can include a negative lens element and a positivelens element which are cemented, and a positive lens element, in thisorder from the object.

In the positive second lens group 20, most of the positive power isdistributed to the cemented lens elements, so that spherical aberrationand coma occurred in the positive second lens group 20 can be correctedsuitably.

The negative third lens group 30 can include negative cemented lenselements and a positive lens element, or, two sets of negative cementedlens elements. More specifically, the negative third lens group 30 caninclude a positive lens element and a negative lens element which arecemented, and a positive lens element having a convex surface facingtoward the image, in this order from the object.

Alternatively, the third lens group 30 can include a positive lenselement and a negative lens element which are cemented, and a negativelens element and a positive lens element which are cemented, in thisorder from the object.

Due to the negative power of the negative third lens group 30, apredetermined negative power can be achieved without occurring sphericalaberration of higher-order and coma of higher-order.

Furthermore, if a positive lens element having a convex surface facingtoward the image is provided at the most image-side of the negativethird lens group 30, the correcting of astigmatism can be madeadequately.

The positive fourth lens group 40 can includes cemented lens elementsand two positive lens elements. More specifically, the positive fourthlens group 40 can include a positive lens element, another positive lenselement and a negative lens element which are cemented, and a positivelens element, in this order from the object.

Alternatively, the positive fourth lens group 40 can include a positivelens element and a negative lens element which are cemented, a positivelens element and a negative lens element which are cemented, and apositive lens element, in this order from the object.

Furthermore, the positive fourth lens group 40 can include threepositive lens elements.

Condition (10) specifies the Abbe number (Np1) of the most object-sidepositive lens element in the positive fourth lens group 40.Np1>70  (10)

The most object-side positive lens element more preferably satisfies thefollowing condition:Np1>80  (10)

Condition (11) specifies the Abbe number (Np2) of the positive lenselement provided in the middle of the positive fourth lens group 40.Np2>65  (11)

By satisfying conditions (10) and (11), the correcting of lateralchromatic aberration can be made adequately and easily.

If an attempt is made to provide a positive lens element on the imageside of the middle positive lens element, and to adequately distributepositive power to the positive lens element (i.e., the most image-sidepositive lens element), the occurrence of spherical aberration and comacan be easily reduced.

Specific numerical data of the embodiments will be describedhereinafter.

In the diagrams of spherical aberration and the sine condition, SAdesignates spherical aberration, and SC designates the sine condition.

In the diagrams of chromatic aberration (axial chromatic aberration)represented by spherical aberration the solid line and the two types ofdotted lines respectively indicate spherical aberrations with respect tothe d, g and C lines.

In the diagrams of lateral chromatic aberration, the two types of dottedlines respectively indicate magnification with respect to the g and Clines; however, the d line as the base line coincides with the ordinate.

In the diagrams of astigmatism, S designates the sagittal image, and Mdesignates the meridional image.

The tables, FNO. designates the f-number, f designates the focal lengthof the entire zoom lens system, W designates the half angle-of-view (°),fB designates the back focal distance, r designates the radius ofcurvature, d designates the lens-element thickness or a distance betweenlens elements (lens groups) which is variable upon zooming, N_(d)designates the refractive index of the d-line, and ν designates the Abbenumber. The values for the distance “d” are indicated in the order ofthe short focal length extremity, an intermediate focal length and thelong focal length extremity.

In addition to the above, an aspherical surface which is symmetricalwith respect to the optical axis is defined as follows:x=cy ²/(1+[1−{1+K}c ² y ²]^(1/2))+A4y ⁴ +A6y ⁶⁺ A8y ⁸⁺ A10y ¹⁰ . . .

wherein:

c designates a curvature of the aspherical vertex (1/r);

y designates a distance from the optical axis;

K designates the conic coefficient; and

A4 designates a fourth-order aspherical coefficient;

A6 designates a sixth-order aspherical coefficient;

A8 designates a eighth-order aspherical coefficient; and

A10 designates a tenth-order aspherical coefficient.

Embodiment 1

FIG. 1 is the lens arrangement of the wide-angle zoom lens system, atthe short focal length extremity, according to the first embodiment ofthe present invention. FIGS. 2A through 2E show aberrations occurred inthe lens arrangement shown in FIG. 1.

FIG. 3 is the lens arrangement of the wide-angle zoom lens system, atthe long focal length extremity, according to the first embodiment ofthe present invention. FIGS. 4A through 4E show aberrations occurred inthe lens arrangement shown in FIG. 3.

Table 1 shows the numerical data of the first embodiment.

The wide-angle zoom lens system of the first embodiment includes anegative first lens group 10, a positive second lens group 20, adiaphragm S, a negative third lens group 30, and a positive fourth lensgroup 40, in this order from the object.

The negative first lens group 10 includes two negative meniscus lenselements each of which has the convex surface facing toward the object,a negative lens element, and a positive lens element, in this order fromthe object. The most object-side negative meniscus lens element is anaspherical lens element made of high-refractive glass.

The positive second lens group 20 includes a positive lens element, apositive lens element and a negative lens element which are cemented, inthis order from the object.

The negative third lens group 30 includes a positive lens element and anegative lens element which are cemented, and a positive lens element,in this order from the object.

The positive fourth lens group 40 includes a positive lens element, apositive lens element and a negative lens element which are cemented,and a positive lens element, in this order from the object.

The diaphragm S is provided 1.50 in front of the negative third lensgroup 30 (surface No. 14). TABLE 1 FNO. = 1:3.6-4.3-5.8 f =12.30-20.00-34.50 W = 50.6-35.3-22.0 fB = 37.90-46.42-59.81 Surf. No. rd Nd ν  1 54.577 1.50 1.80500 34.9  2* 25.604 2.21 — —  3 36.010 1.501.80500 46.8  4 18.205 11.41  — —  5 402.624 1.80 1.64610 57.2  6*25.534 3.92 — —  7 39.824 3.00 1.84697 23.9  8 123.764 34.57-14.05-2.50— —  9 44.796 2.72 1.55374 43.8 10 331.611 0.10 — — 11 27.991 3.641.48749 70.2 12 −19.756 1.00 1.80518 25.4 13 −33.364 3.70-7.91-17.83 — —14 −33.026 2.40 1.77194 26.4 15 −10.635 1.00 1.77250 48.5 16 26.496 0.00— — 17 23.806 1.90 1.62489 35.5 18 167.952 7.70-6.61-2.20 — — 19 161.5684.22 1.56907 71.3  20* −15.157 0.10 — — 21 −21.560 4.48 1.48749 70.2 22−11.516 1.00 1.80518 25.4 23 −37.857 0.10 — — 24 −635.386 3.14 1.5755243.0 25 −30.202 — — —The symbol * designates the aspherical surface which is rotationallysymmetrical with respect to the optical axis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 A10 2 0.00 −0.21794 ×10⁻⁴  0.20397 × 10⁻⁷ −0.28748 × 10⁻¹⁰ −0.30884 × 10⁻¹⁴ 6 0.00  0.11273 ×10⁻⁴ −0.15720 × 10⁻⁶  0.54287 × 10⁻⁹ −0.12197 × 10⁻¹¹ 20 0.00  0.14232 ×10⁻⁴  0.54971 × 10⁻⁷ −0.37930 × 10⁻⁹

Embodiment 2

FIG. 5 is the lens arrangement of the wide-angle zoom lens system, atthe short focal length extremity, according to a second embodiment ofthe present invention. FIGS. 6A through 6E show aberrations occurred inthe lens arrangement shown in FIG. 5.

FIG. 7 is the lens arrangement of the wide-angle zoom lens system, atthe long focal length extremity, according to the second embodiment ofthe present invention. FIGS. 8A through 8E show aberrations occurred inthe lens arrangement shown in FIG. 7.

Table 2 shows the numerical data of the second embodiment.

The wide-angle zoom lens system of the second embodiment includes anegative first lens group 10, a diaphragm S, a positive second lensgroup 20, a negative third lens group 30, and a positive fourth lensgroup 40, in this order from the object.

The negative first lens group 10 includes two negative meniscus lenselements each of which has the convex surface facing toward the object,a positive meniscus lens element having the convex surface facing towardthe object, a biconcave negative lens element, and a positive lenselement, in this order from the object. The most object-side negativemeniscus lens element is an aspherical lens element made ofhigh-refractive glass.

The positive second lens group 20 includes a negative lens element and apositive lens element which are cemented, and a positive lens element,in this order from the object.

The negative third lens group 30 includes a positive lens element and anegative lens element which are cemented, and a negative lens elementand a positive lens element which are cemented, in this order from theobject.

The positive fourth lens group 40 includes a positive lens element,cemented lens elements having a positive lens element and a negativelens element, and a positive lens element, in this order from theobject. On the object-side surface of the most image-side lens positiveelement of the positive fourth lens group 40, an aspherical layer madeof synthetic resign is formed.

The diaphragm S is provided 1.44 in front of the second lens group 20(surface No. 11) on the optical axis. TABLE 2 F = 1:3.6-4.1-4.6 f =12.30-20.00-34.50 W = 50.5-35.3-22.1 fB = 37.88-46.97-61.92 Surf. No. rd Nd ν  1* 83.806 2.20 1.77250 49.6  2 23.704 4.80 — —  3 42.658 1.701.77200 49.6  4 21.410 4.20 — —  5 55.556 1.50 1.80400 41.1  6* 60.0747.70 — —  7 −78.903 1.60 1.80400 46.6  8 29.209 1.61 — —  9 32.968 3.551.74935 27.6 10 −536.613 29.61-13.12-3.94 — — 11 36.070 1.00 1.8051825.4 12 17.456 4.51 1.55202 51.1 13 −51.973 0.10 — — 14 23.284 3.501.49700 81.6 15 −100.265 2.96-6.27-11.77 — — 16 −67.918 2.23 1.8469923.8 17 −15.648 1.20 1.80610 40.9 18 70.896 1.09 — — 19 −38.916 1.001.80400 46.6 20 16.575 2.86 1.68419 30.8 21 −136.202 9.36-6.88-2.20 — —22 47.505 4.49 1.49700 81.6 23 −18.378 0.10 — — 24 −80.669 5.03 1.4978868.9 25 −13.545 1.00 1.79973 28.9 26 −63.739 0.10 — —  27* −523.909 0.101.52972 42.7 28 −523.909 2.34 1.48749 70.2 29 −41.321 — — —The symbol * designates the aspherical surface which is rotationallysymmetrical with respect to the optical axis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 A10 1 0.00  0.16843 ×10⁻⁴ −0.20067 × 10⁻⁷  0.14141 × 10⁻¹⁰ 0.75460 × 10⁻¹⁴ 6 0.00  0.97713 ×10⁻⁵  0.67160 × 10⁻⁸ −0.25828 × 10⁻⁹ 0.85535 × 10⁻¹² 27 0.00 −0.13257 ×10⁻⁴  0.16564 × 10⁻⁷

Embodiment 3

FIG. 9 is the lens arrangement of the wide-angle zoom lens system, atthe short focal length extremity, according to the third embodiment ofthe present invention. FIGS. 10A through 10E show aberrations occurredin the lens arrangement shown in FIG. 9.

FIG. 11 is the lens arrangement of the wide-angle zoom lens system, atthe long focal length extremity, according to the third embodiment ofthe present invention. FIGS. 12A through 12E show aberrations occurredin the lens arrangement shown in FIG. 11.

Table 3 shows the numerical data of the third embodiment.

The wide-angle zoom lens system of the third embodiment includes anegative first lens group 10, a positive second lens group 20, adiaphragm S, a negative third lens group 30, and a positive fourth lensgroup 40, in this order from the object.

The negative first lens group 10 includes two negative meniscus lenselements each of which has the convex surface facing toward the object,a positive lens element, a biconcave negative lens element, and apositive lens element, in this order from the object.

The object-side negative meniscus lens element is an aspherical lenselement made of high-refractive glass.

On the image-side surface of the biconcave negative lens element, anaspherical layer made of synthetic resin is formed.

The remaining lens arrangement is the same as that of the secondembodiment.

The diaphragm S is provided 0.00 in front of the second lens group 20(surface No. 16) on the optical axis. TABLE 3 F = 1:3.6-4.0-4.5 f =12.30-18.00-34.50 W = 50.6-38.2-22.0 fB = 39.22-44.89-60.46 Surf. No. rd Nd ν  1* 85.912 2.50 1.74320 49.3  2 24.220 5.11 — —  3 48.112 1.701.72916 54.7  4 21.410 6.08 — —  5 478.645 1.94 1.60000 38.5  6 −478.6454.72 — —  7 −164.558 1.80 1.80400 46.6  8 33.368 0.10 1.52972 42.7  9*33.368 2.05 — — 10 29.351 3.29 1.56940 42.3 11 139.546 26.74-13.71-2.50— — 12 45.047 1.00 1.84666 23.8 13 15.951 4.14 1.55555 47.3 14 −74.9030.13 — — 15 24.131 3.82 1.59016 39.5 16 −45.596 3.14-6.11-13.01 — — 17−56.686 2.23 1.80500 25.4 18 −13.955 1.00 1.79904 40.6 19 63.472 1.15 —— 20 −28.212 1.00 1.80400 46.6 21 15.849 2.82 1.76588 26.8 22 −68.95310.21-8.22-2.20 — — 23 37.898 4.55 1.49700 81.6 24 −19.279 0.11 — — 25−116.020 5.03 1.48749 70.2 26 −13.720 1.00 1.80518 25.4 27 −127.012 0.44— —  28* −88.633 0.10 1.52972 42.7 29 −88.633 2.92 1.48749 70.2 30−23.390 — — —The symbol * designates the aspherical surface which is rotationallysymmetrical with respect to the optical axis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 A10 1 0.00  0.12372 ×10⁻⁴ −0.14118 × 10⁻⁷ 0.14420 × 10⁻¹⁰ −0.47374 × 10⁻¹⁴ 9 0.00  0.11888 ×10⁻⁴ −0.63772 × 10⁻⁷ 0.62109 × 10⁻¹⁰  0.47949 × 10⁻¹² 28 0.00 −0.22881 ×10⁻⁴ −0.34462 × 10⁻⁸ 0.94666 × 10⁻¹⁰

Embodiment 4

FIG. 13 is the lens arrangement of the wide-angle zoom lens system, atthe short focal length extremity, according to a fourth embodiment ofthe present invention. FIGS. 14A through 14E show aberrations occurredin the lens arrangement shown in FIG. 13.

FIG. 15 is the lens arrangement of the wide-angle zoom lens system, atthe long focal length extremity, according to the fourth embodiment ofthe present invention. FIGS. 16A through 16E show aberrations occurredin the lens arrangement shown in FIG. 15.

Table 4 shows the numerical data of the fourth embodiment.

The negative first lens group 10 includes a biconvex positive lenselement, two negative meniscus lens elements each of which has theconvex surface facing toward the object, a negative lens element, and apositive lens element, in this order from the object.

On the image-side surface of the negative lens element, an asphericallayer made of synthetic resin is formed.

The image-side negative meniscus lens element is an aspherical lenselement made of synthetic resin.

The remaining lens arrangement is the same as that of the secondembodiment.

The diaphragm S is provided 1.00 in front of the third lens group 30(surface No. 17) on the optical axis. TABLE 4 F = 1:3.6-4.0-5.9 f =12.30-18.00-34.50 W = 50.6-38.8-22.2 fB = 37.90-44.27-63.27 Surf. No. rd Nd ν  1 472.110 2.55 1.80500 39.1  2 −1687.632 0.20 — —  3 71.142 2.001.80400 46.6  4 18.101 6.76 — —  5 40.578 2.20 1.52538 56.3  6* 19.0009.72 — —  7 380.093 1.80 1.77250 49.9  8 21.914 0.20 1.52972 42.7  9*21.914 0.50 — — 10 21.732 4.33 1.60100 37.9 11 188.578 28.88-15.13-2.74— — 12 40.496 1.20 1.84666 23.8 13 16.523 3.34 1.54256 46.7 14 −53.5915.83 — — 15 29.502 2.98 1.55205 46.3 16 −42.055 3.12-6.36-13.31 — — 17−60.277 2.02 1.80518 25.4 18 −16.901 1.10 1.80400 46.6 19 69.174 0.85 —— 20 −37.477 1.10 1.75695 42.2 21 19.810 2.06 1.80518 25.4 22 −174.26612.39-9.15-2.20 — — 23 34.447 4.64 1.49700 81.6 24 −23.203 0.10 — — 25726.371 5.25 1.48749 70.2 26 −15.244 1.20 1.83500 29.1 27 69.568 0.74 ——  28* 190.169 0.10 1.52972 42.7 29 190.169 4.26 1.48749 70.2 30 −21.270— — —The symbol * designates the aspherical surface which is rotationallysymmetrical with respect to the optical axis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 6 0.00 −0.34238 × 10⁻⁴−0.71547 × 10⁻⁸ −0.10324 × 10⁻⁹ 9 0.00 −0.77559 × 10⁻⁶ −0.45921 × 10⁻⁷ 0.24198 × 10⁻¹⁰ 28 0.00 −0.23297 × 10⁻⁴  0.19028 × 10⁻⁸  0.14837 × 10⁻⁹

Embodiment 5

FIG. 17 is the lens arrangement of the wide-angle zoom lens system, atthe short focal length extremity, according to the fifth embodiment ofthe present invention. FIGS. 18A through 18E show aberrations occurredin the lens arrangement shown in FIG. 17.

FIG. 19 is the lens arrangement of the wide-angle zoom lens system, atthe long focal length extremity, according to the fifth embodiment ofthe present invention. FIGS. 20A through 20E show aberrations occurredin the lens arrangement shown in FIG. 19.

Table 5 shows the numerical data of the fifth embodiment.

The negative first lens group 10 includes a biconvex positive lenselement, two negative meniscus lens elements each of which has theconvex surface facing toward the object, and cemented lens elementshaving a positive lens element and a negative lens element, in thisorder from the object.

The image-side negative meniscus lens element is an aspherical lenselement made of synthetic resin.

On the most object-side surface of the cemented lens elements, anaspherical layer made of synthetic resin is formed.

The positive fourth lens group 40 includes a positive lens element and anegative lens element which are cemented, a positive lens element and anegative lens element which are cemented, and a positive lens element,in this order from the object. On the object-side surface of the mostimage-side lens positive element of the positive fourth lens group 40,an aspherical layer made of synthetic resign is formed.

The remaining lens arrangement is the same as that of the secondembodiment.

The diaphragm S is provided 0.23 in front of the third lens group 30(surface No. 16) on the optical axis. TABLE 5 F = 1:3.6-4.0-5.9 f =12.30-18.01-34.50 W = 50.6-38.5-22.1 fB = 37.90-43.57-61.25 Surf. No. rd Nd ν  1 598.572 2.88 1.53172 48.9  2 −598.572 0.20 — —  3 80.290 2.001.80400 46.6  4 18.158 5.78 — —  5 30.961 2.20 1.52538 56.3  6* 17.50011.18 — —  7* 208.181 0.20 1.52972 42.7  8 102.440 1.50 1.80400 46.6  924.291 5.60 1.71736 29.5 10 90.685 26.39-13.76-2.50 — — 11 60.821 1.201.84666 23.8 12 17.218 3.52 1.54072 47.2 13 −59.294 1.25 — — 14 24.8323.01 1.59551 39.2 15 −49.682 3.03-6.86-15.01 — — 16 −81.614 2.02 1.8051825.4 17 −19.812 1.10 1.80400 46.6 18 86.641 0.80 — — 19 −37.350 1.101.78590 44.2 20 13.396 3.09 1.80610 33.3 21 −237.163 14.17-10.34-2.20 —— 22 35.712 5.63 1.49700 81.6 23 −16.243 1.20 1.83400 37.2 24 −21.4560.10 — — 25 227.248 4.86 1.49700 81.6 26 −19.929 1.00 1.80610 33.3 27103.850 0.98 — —  28* −620.276 0.10 1.52972 42.7 29 −620.276 3.561.48749 70.2 30 −26.123 — — —The symbol * designates the aspherical surface which is rotationallysymmetrical with respect to the optical axis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 6 0.00 −0.35544 × 10⁻⁴−0.27224 × 10⁻⁷ −0.19752 × 10⁻¹⁰ 7 0.00  0.64089 × 10⁻⁵  0.34632 × 10⁻⁷ 0.17295 × 10⁻⁹ 28 0.00 −0.24048 × 10⁻⁴ −0.23473 × 10⁻⁷  0.17971 × 10⁻¹⁰

The numerical values of each condition for each embodiment are shown inTable 6. TABLE 6 Embod. 1 Embod. 2 Embod. 3 Embod. 4 Embod. 5 Cond. (1)2.48 2.34 1.88 2.06 1.89 Cond. (2) 1.67 1.36 1.38 1.30 1.36 Cond. (3)2.33 1.89 1.85 1.99 2.01 Cond. (4) 1.07 1.24 1.02 1.03 0.94 Cond. (5)2.13 3.86 4.20 3.46 3.06 Cond. (6) 1.39 1.39 1.34 1.53 1.48 Cond. (7)1.05 1.45 1.46 1.43 1.28 Cond. (8) 0.63 0.75 0.78 0.61 0.59 Cond. (9)0.83 0.72 0.72 0.66 0.69

As can be understood from Table 6, the first through fifth embodimentssatisfy conditions (1) through (9). Furthermore, as can be understoodfrom the aberration diagrams, the various aberrations are adequatelycorrected.

According to the above description, a wide-angle zoom lens system havingthe following features can be obtained:

(i) being suitable for a digital SLR camera having a smaller imagingdevice;

(ii) the angle-of-view of approximately 100 degrees at the short focallength extremity; and

(iii) a zoom ratio of approximately 2.5 through 3.0.

Obvious changes may be made in the specific embodiments of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

1. A wide-angle zoom lens system comprising a negative first lens group,a positive second lens group, a negative third lens group and a positivefourth lens group, in this order from an object; wherein upon zoomingfrom the short focal length extremity to the long focal lengthextremity, a distance between said negative first lens group and saidpositive second lens group decreases, a distance between said positivesecond lens group and said negative third lens group increases, and adistance between said negative third lens group and said positive fourthlens group decreases; and wherein said wide-angle zoom lens systemsatisfies the following conditions:1.6<X2/fw<3.51.2<|f1|/fw<2.0 (f1<0)1.6<f2/fw<2.7 wherein X2 designates the traveling distance of saidpositive second lens group upon zooming from the short focal lengthextremity to the long focal length extremity; f1 designates the focallength of said negative first lens group; f2 designates the focal lengthof said positive second lens group; and fw designates the focal lengthof the entire wide-angle zoom lens system at the short focal lengthextremity.
 2. The wide-angle zoom lens system according to claim 1,further satisfying the following condition:0.9<X2/f2<1.6 wherein X2 designates the traveling distance of saidpositive second lens group upon zooming from the short focal lengthextremity to the long focal length extremity; and f2 designates thefocal length of said positive second lens group.
 3. The wide-angle zoomlens system according to claim 1, further satisfying the followingconditions:2.0<fBw×fBw/(f1×f3)<6.01.2<f2/|f1|<1.81.0<f4/|f3|<1.8 wherein fBw designates the equivalent air thickness fromthe most image-side lens surface to the image plane at the short focallength extremity; f1 designates the focal length of said negative firstlens group; f2 designates the focal length of said positive second lensgroup; f3 designates the focal length of said negative third lens group;and f4 designates the focal length of said positive fourth lens group.4. The wide-angle zoom lens system according to claim 1, furthersatisfying the following conditions:0.5<f1/f3<0.90.6<f2/f4<0.9 wherein f3 designates the focal length of said negativethird lens group; and f4 designates the focal length of said positivefourth lens group.
 5. The wide-angle zoom lens system according to claim1, wherein said negative first lens group comprises a negative meniscuslens element having the convex surface facing toward the object, anothernegative meniscus lens element having the convex surface facing towardthe object, a negative lens element having a concave surface facingtoward an image and a positive lens element, in this order from theobject.
 6. The wide-angle zoom lens system according to claim 1, whereinsaid negative first lens group comprises a positive lens element, anegative meniscus lens element having the convex surface facing towardthe object, another negative meniscus lens element having the convexsurface facing toward the object, a negative lens element having aconcave surface facing toward an image and a positive lens element, inthis order from the object.
 7. The wide-angle zoom lens system accordingto claim 1, wherein said positive second lens group comprises positivecemented lens elements and a positive lens element.
 8. The wide-anglezoom lens system according to claim 1, wherein said negative third lensgroup comprises negative cemented lens elements and a positive lenselement, or, two sets of negative cemented lens elements.
 9. Thewide-angle zoom lens system according to claim 1, wherein said positivefourth lens group comprises cemented lens elements and two positive lenselements.
 10. A wide-angle zoom lens system comprising a negative firstlens group, a positive second lens group, a negative third lens groupand a positive fourth lens group, in this order from an object; whereinupon zooming from the short focal length extremity to the long focallength extremity, a distance between said negative first lens group andsaid positive second lens group decreases, a distance between saidpositive second lens group and said negative third lens group increases,and a distance between said negative third lens group and said positivefourth lens group decreases; and wherein said wide-angle zoom lenssystem satisfies the following conditions:2.0<fBw×fBw/(f1×f3)<6.01.2<f2/|f1|<1.81.0<f4/|f3|<1.8 wherein fBw designates the equivalent air thickness fromthe most image-side lens surface to the image plane at the short focallength extremity; f1 designates the focal length of said negative firstlens group; f2 designates the focal length of said positive second lensgroup; f3 designates the focal length of said negative third lens group;and f4 designates the focal length of said positive fourth lens group.11. The wide-angle zoom lens system according to claim 10, furthersatisfying the following conditions:0.5<f1/f3<0.90.6<f2/f4<0.9
 12. The wide-angle zoom lens system according to claim 10,wherein said negative first lens group comprises a negative meniscuslens element having the convex surface facing toward the object, anothernegative meniscus lens element having the convex surface facing towardthe object, a negative lens element having a concave surface facingtoward an image and a positive lens element, in this order from theobject.
 13. The wide-angle zoom lens system according to claim 10,wherein said negative first lens group comprises a positive lenselement, a negative meniscus lens element having the convex surfacefacing toward the object, another negative meniscus lens element havingthe convex surface facing toward the object, a negative lens elementhaving a concave surface facing toward an image and a positive lenselement, in this order from the object.
 14. The wide-angle zoom lenssystem according to claim 10, wherein said positive second lens groupcomprises positive cemented lens elements and a positive lens element.15. The wide-angle zoom lens system according to claim 10, wherein saidnegative third lens group comprises negative cemented lens elements anda positive lens element, or, two sets of negative cemented lenselements.
 16. The wide-angle zoom lens system according to claim 10,wherein said positive fourth lens group comprises cemented lens elementsand two positive lens elements.